murph the surf

You're right-that would have looked great...

Yes

Logical answer, but that's not the customer option that was offered at the very same time the additional rear axle ratios were offered..

What was the other item offered in the Avanti Order Guide as a new option for the Studebaker Avanti customer, offered at the same time additional customer options for rear axle ratio selection became available, and why was this new option offered ?

Bingo!.....813 refers to the new solid black interior, first offered in May, 1963..

"813" referred to what component of the Studebaker Avanti?

Ah, a radial spare won't fit in the spare tire well..

Wheels not able to handle the flexing that radial tires can cause. A side effect is wheel covers not staying on properly...